I wanted to do a "summer lightweight quilt" as well, and another more experienced quilter than I am suggested I use 100% bleached or unbleached muslin for the batting. Because it's all cotton, and my top and bottom would be all cotton, the quilt would still 'breathe', and the muslin would add very little weight. But like the others, I don't see why you couldn't just put the two layers together. This was just a suggestion.